This application is a continuation-in-part application Ser. No. 07/525,020 filed May 18, 1990 by the same inventors.
1. Field of the Invention
This invention relates to the use of recycle multilayer heat shrinkable polymeric film along with virgin polymer to form multilayer heat shrinkable film having attractive shrinkage force.
2. Description of Related Art
U.S. Pat. No. 4,532,189 discloses a heat shrinkable film of a core layer sandwiched between coextruded skin layers. The core layer is disclosed to consist of at least 10% of LLDPE or LMDPE blended with 0 to 90% of ethylene/propylene copolymer or with other ethylene copolymers or LDPE in varying amounts. LLDPE is disclosed to mean linear low density polyethylene, which is further disclosed to mean a copolymer of ethylene and 8% or less of butene, octene, or hexene, and having a density of from 0.910 to 0.925 g/cc.sup.3. Ethylene propylene copolymer is disclosed to mean such copolymer wherein propylene is present as a major constituent and ethylene is present as a minor constituent. LDPE is disclosed to be a homopolymer of ethylene. The skin layers are disclosed to be ethylene propylene copolymer or blends of ethylene propylene copolymer with other specific polymers, e.g. polypropylene, with the preferred skin layers having a composition of 80% ethylene propylene copolymer and 20% polypropylene. The preferred core layer is disclosed to consist essentially of LLDPE. The patent also discloses five-layer heat shrinkable film in which intermediate layers are present between the core layer and skin layers.
U.S. Pat. No. 4,837,084 discloses heat shrinkable film suitable for bags and pouches. The film is disclosed to comprise at least one layer of a copolymer of ethylene and an alpha-olefin with 6 or more carbon atoms per molecule and having a density of about 0.910 g/cc or less and melt index of about 2 or less. The patent discloses that these copolymers belong to the class of polymers known as very low density linear polyethylene (VLDPE). In Table I, ethylene copolymers (with octene) having densities of 0.911 and 0.912 g/cc are disclosed to be a comparison example and to come from a different class, namely the class called LLDPE. The patent also discloses that the VLDPE can be blended with up to 50% by weight with ethylene acrylate copolymer, LLDPE, HDPE, LMDPE, LHDPE, LDPE, MDPE, EVA, acid modified EVA, PP, ethylene/propylene copolymers, copolymers of certain alpha-olefins with certain carboxylic acids. For one embodiment, the patent discloses positioning the VLDPE layer between a heat sealing layer and an outside layer and that the heat sealing layer can consist of the other polymers that can be used in the VLDPE layer as well as many more polymers disclosed. The Examples in the patent, however, disclose the sealing layer to be primarily coextruded EVA copolymer, wherein the coextruded inner layer and heat sealing layer are subjected to irradiation. Barrier and outside layers are then extruded onto the radiation crosslinked coextrudate. Radiation involved in making this four-layer heat shrinkable film prevents scrap from the film from being recycled by melt processing, e.g. extrusion.
U.S. Pat. No. 4,439,478 discloses a heat shrinkable film of a base layer of propylene homopolymer and at least one skin layer of a blend of propylene-ethylene copolymer with 20 to 40% by weight of propylene homopolymer, the base layer being at least 4 times the thickness of the skin layer.
Cryovac MPD-2055 heat shrinkable film is available from W. R. Grace and Company. This film is understood to consist of a core layer of LLDPE sandwiched between two outer layers of propylene ethylene copolymer in which the ethylene constitutes about 3% of the weight of the copolymer. The two outer layers constitute 50% of the weight of the film, and the film does not appear to have been irradiated.
The need exists for heat shrinkable film having high shrinkability upon application of heat, typically 110.degree. C., and low shrinkage force and which can use scrap multilayer heat shrinkable film for recycling by melt processing along with virgin thermoplastic polymer into heat shrinkage film.